Three columns, A, B, and C, are collinear, 500 mm in diameter, and 2.0 m on-center. Theyhave unfactored vertical downward loads of 1,000, 550, and 700 kN, respectively, and are to be supported on a single, 1.0 m deep rectangular combined footing. The soil beneath this pro-posed footing has the following properties: g = 19.5 kN/m3 , c′ = 10 kPa, and f′ = 31o. The groundwater table is at a depth of 25 m below the ground surface.a. Using ASD, determine the minimum footing length, L, and the placement of the columnson the footing that will place the resultant load at the centroid of the footing. The footingmust extend at least 500 mm beyond the edges of columns A and C. b. Using the results from part (a), determine the minimum footing width, B, that will main-tain a factor of safety of 2.5 against a bearing capacity failure. Show the final design in a sketch.Hint: Assume a value for B, compute the allowable bearing capacity, then solve for B. Repeatthis process until the computed B is approximately equal to the assumed B.
Three columns, A, B, and C, are collinear, 500 mm in diameter, and 2.0 m on-center. They
have unfactored vertical downward loads of 1,000, 550, and 700 kN, respectively, and are to
be supported on a single, 1.0 m deep rectangular combined footing. The soil beneath this pro-
posed footing has the following properties: g = 19.5 kN/m3
, c′ = 10 kPa, and f′ = 31o
. The
groundwater table is at a depth of 25 m below the ground surface.
a. Using ASD, determine the minimum footing length, L, and the placement of the columns
on the footing that will place the resultant load at the centroid of the footing. The footing
must extend at least 500 mm beyond the edges of columns A and C.
b. Using the results from part (a), determine the minimum footing width, B, that will main-
tain a factor of safety of 2.5 against a bearing capacity failure. Show the final design in a
sketch.
Hint: Assume a value for B, compute the allowable bearing capacity, then solve for B. Repeat
this process until the computed B is approximately equal to the assumed B.
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